1. Field of the Invention
The present invention generally relates to an anti-corrosion or corrosion-resistant finish and method(s) of forming the finish. More particularly, the present invention relates to a corrosion-resistant finish primarily for use in automobile applications, which finish comprises multiple layers, including a zinc-iron substrate layer, a phosphate crystal conversion layer, and a fluorocarbon sealer coat layer.
2. Description of the Prior Art
In their 1996 article, “Alternative to Hexavalent Chrome,” the Institute of Manufacturing Sciences wrote, as follows: “Fugitive air emissions, water emissions from poorly treated rinse water, and solid waste generated from hexavalent chromium processes can have a detrimental impact on the environment. This impact can be eliminated or reduced if a cleaner technology is used.” In response to this article, the European Union and the European Communities wrote two directives.
The first directive (European Union Directive on End of Life Vehicles COM(97) 0358-C4-0639/97-97/0194(SYN), Sep. 18, 2000, “2000/53/EC and Draft: Amending Annex II of Directive 2000/53/EC”, (1) The reuse/recovery of End of Life Vehicles (ELV's) to reach 85% by weight per vehicle by 2006 and 95% by 2015, and (2) The reuse/recycling of ELV's to reach 80% by weight per vehicle by 2006 and 85% by 2015) was a legislative attempt to reduce the amount of ELV waste that is land filled or incinerated without energy recovery. This legislation was enacted in response to findings that showed ELV shredding residue comprises approximately 60% of the total shredding residues in Europe. It is thus generally accepted that reducing the amount of hazardous shredding residue from ELV's will have a positive impact on the environment.
The second directive (European Communities Directive: 67/548/EEC) attempts to regulate the classification, packaging, and labeling of hexavalent chromium and other dangerous substances. In the United Kingdom and Japan, for example, Cr+6 compounds are identified as Category 1 carcinogens. The governments of both the United Kingdom and Japan thus require facilities utilizing products containing hexavalent chromium compounds to implement reduction and elimination programs.
The North American auto manufacturers have responded to the directives from overseas by writing new “Restrictive and Reportable Substances” specifications. The projected implementation dates for the new global standards (i.e. the projected implementation dates for the elimination of hexavalent chrome (Cr+6) from vehicles) as adopted by the major North American automobile manufacturers and as prompted by the European Union Directives, are as follows:
General Motors:
    GMW3059 Implementation on Model Year 2006    Exception: Opal and Saab Divisions: Implementation on calendar date Jan. 1, 2005Daimler Chrysler:    Hexavalent Systems will no longer be allowed or covered under Daimler Chrysler Process Standards beginning Jan. 1, 2007. On this date, all systems shall be converted to Trivalent Chromium processes ONLY.Ford Body & Chassis: & Visteon/Ford:    Ford Motor WSS-M9P99999-A1 (known as the Hex 9 spec.)    Implementation on calendar date Jul. 31, 2005Delphi Automotive:    DX000001: Implementation on calendar date Jan. 1, 2007    However, PPAPs in March and April of 2006 will implement DX000001Nissan:    NES M 0301: Implementation on calendar date Jul. 1, 2003Toyota:    Spec. # is currently under evaluation: Implementation on calendar date Jul. 1, 2007European Union Directives    COM(97) 0358-C4-0639/97-97/0194(SYN) 67/548/EEC (2000/53/EC)    Draft: Amending Annex II of Directive 2000/53/EC    Implementation on calendar date Jul. 1, 2007
Since the first inception of these directives one of the challenges in the automotive industry has been to develop a hexavalent chrome-free, or a totally chrome-free, black, corrosion finish that can withstand extended corrosion testing. Thus, the premise of the present invention is to provide a plating or coating system that meets the specified criteria. Some of the more pertinent requirements of a plating or coating system are that the plating/coating (1) must be black; (2) must be Cr (VI) free (Hexavalent Chrome Free), or totally chrome-free; (3) must be able to withstand a minimum of 1500 hrs salt spray testing to red corrosion; (4) must be able to withstand a minimum of 500 hrs salt spray testing to white corrosion; (5) must have a lubricity factor or coefficient of friction (k<0.13) (in particular, no squeaking can occur in plastic molded assemblies); (6) must be able to withstand injection molding temperatures of 700–750° F. (371–399° C.) for an intermittent cycle time of 10–30 seconds. And a continuous service temperature range of 450–550° F. (371–399° C.) with no breakdown in its corrosion properties; and (7) must not fill in the head recesses or threads of the fasteners.
The fastener industry applies corrosion protection systems to approximately 90% of its manufactured product. In general the main type of corrosion protection system used on fasteners is an electrogalvanizing deposit of zinc followed by a sealing polymeric sheath or envelope (chromates). The salt spray protection to red corrosion in these types of systems ranges from 48 to 168 hours. With the inception of the automotive directives many of the new corrosion systems in the industry have turned to trivalent (CrIII) chromates, and top coat sealers.
One of the ways to significantly improve corrosion resistance in an electroplating system is to adjoin a heavy metal atom to the zinc (iron-carbon) galvanic process. The three most common zinc alloying metals are cobalt, nickel, and iron. In theory the tiny additions of these alloying elements prevent, or delay the startup of intergranular corrosion of the zinc. The results are that red corrosion resistance is increased to 425 hours and up to 1000 hours in these plating systems. Many of these plating systems however, have hexavalent chromium in their top chromate sealers.
For this design premise the metal atom group of most interest is the zinc-iron plating system. This system will provide a proper substrate layer for the attachment of a heat barrier coating layer. An additional fluorocarbon top sealer will provide the desired coefficient of friction requirement, and complete the total corrosion protection system.
For purposes of comparison the reader is directed to U.S. Pat. No. 6,318,898 ('898 Patent), which issued to Ward et al. The '898 Patent discloses a Corrosion-Resistant Bearing and Method for Making Same and thus teaches a corrosion-resistant antifriction bearing that includes a multi-layer corrosion protection system over a metallic substrate. The corrosion-resistant system may be applied to a single or multiple components of the bearing, including inner and outer rings, bearing elements, collars, and so forth. The system includes a nickel-phosphorous alloy plating layer applied by an autocatalytic process after surface preparation of the protected component. The surface preparation aids in adherence of the nickel-phosphorous alloy plating layer to the substrate. The preparation may include the application of rust inhibitors, liquid vapor honing, acid neutralizing, and so forth. Additional top coat layers may be applied to the nickel-phosphorous allow plating layer. These may include a chromate conversion coating and a polymeric top coat layer. The polymeric top coat layer may include polytetrafluoroethylene. U.S. Pat. No. 6,146,021 ('021 Patent), also issued to Ward, teaches related subject matter to the '898 Patent.
The reader is further directed to U.S. Pat. No. 6,562,474 ('474 Patent), which issued to Yoshimi et al. The '474 Patent discloses a Coated Steel Sheet having Excellent Corrosion Resistance and Method for Producing the Same. The '474 Patent teaches a coated steel sheet having excellent corrosion resistance comprises: a zinc or a zinc alloy plated steel sheet or an aluminum or an aluminum alloy plated steel sheet; a composite oxide coating formed on the surface of the plated steel sheet; and an organic coating formed on the composite oxide coating. The composite oxide coating contains a fine particle oxide and a phosphoric acid and/or a phosphoric acid compound. The organic coating has thickness of from 0.1 to 5 .mu.m. Notably, the organic coating may, at need, further include a solid lubricant (c) to improve the workability of the coating. Examples of applicable solid lubricant according to the present invention are the following. (1) Polyolefin wax, paraffin wax: for example, polyethylene wax, synthetic paraffin, natural paraffin, microwax, chlorinated hydrocarbon; (2) Fluororesin fine particles: for example, polyfluoroethylene resin (such as polytetrafluoroethylene resin), polyvinylfluoride resin, polyvinylidenefluoride resin.
From a review of these prior art disclosures and from a general consideration of other well known prior art teachings, it will be seen that the prior art does not teach a black, chrome-free, multilayer, corrosion protection system designed to meet a minimum of 500 salt spray testing hours to white corrosion, and 1500 salt spray testing hours to red corrosion when tested to ASTM B 117 standards for use on automotive body sheet steel, automotive underbody parts, automotive under-hood parts, and some automotive interior parts specifying a gloss requirement greater than 4. Further, it will be seen that the prior art does not teach a chrome-free, multilayer system comprising a combination of a zinc-iron electroplated substrate, a non-electrolytic phosphate crystal conversion layer using orthophosphoric acid, and a Xylan Teflon/fluorocarbon sealer coating to form a three layer total corrosion protection system.